Surface Enhancements

Vistamaxx^TM specialty elastomers are a new generation of metallocene catalyst based specialty polyolefin elastomers (SPE) that can be processed in conventional spunmelt equipment to produce elastic nonwoven fabrics. For applications involving elastic components in the hygiene absorbent products market, the touch and aesthetic properties of the SPE based nonwoven are important.

This paper examines modification of the surface properties of spunmelt SPE nonwovens through the use of additives that can be added in line during melt spinning.  The additives considered are conventional slip additives such as erucamide, hydrocarbon resins and other surface modifying additives such as high melt flow polypropylene, polyolefin waxes, as well as inorganic particulates and combinations of slip with surface modifying additives.   The slip, which is formulated as a masterbatch in the SPE carrier is added to provide an effective concentration between 3,000 to 6,000 ppm in the elastic nonwoven.  The presence of the slip additive either by itself or in combination with the polyolefin surface modifiers provides a touch that is markedly different from the base SPE touch that has been described as "rubbery", without sacrificing the intrinsic elastic property of the SPE nonwoven.

The elastic properties of the modified SPE nonwovens are measured using cyclic testing to an extension of 100 % strain and returned to zero load. The permanent set, load loss and mechanical hysteresis are measured after the first and second cycle. The surface chemistry and morphology of the nonwoven fibers is characterized using an array of different surface sensitive analytical techniques -  Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy(XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Scanning Electron Microscopy (SEM). Addition of slip and low molecular weight polyolefins show a distinct migration tendency to the fiber surface due either to viscosity mismatches relative to the SPE resin, or due to a thermodynamic incompatibility with the SPE resin, thereby imparting a touch that is different from the unmodified SPE. 

The addition of surface modifying additives is an effective way to adjust the surface features of the elastic nonwoven, resulting in the ability to tailor the surface feel of the nonwoven. Further custom tailoring by various combinations of the modifiers is an extension of this effort that can be conducted by the nonwoven manufacturers.

Polypropylene (PP) fibers, widely utilized in woven and nonwoven industry, have highly inert and hydrophobic surfaces. Therefore a modification aimed at the creation of a more polar surface is an important issue in the application areas where wettability and adhesion properties are required. One way to impart surface hydrophilicity into polypropylene is blending of the melt additives prior to or during fiber spinning process. It is reported that some oligomeric melt additives spun with host polymer migrate to surface and generate surface reactivity at low concentration without altering bulk properties.

We investigated surface segregation of ethoxylated melt additives in polypropylene polymers and its impact on surface properties. Surface composition of melt additive containing polypropylene was investigated with surface specific analysis method such as XPS and surface hydrophilicity is measured with dynamic water contact angle. We found that surface enrichment of additives lead to hydrophilic polypropylene surfaces and additive molecular characteristics such as hydrophilic or hydrophobic group size impact additive migration behavior and surface hydrophilicity. We also found that resulting surface characteristics are very dynamic, so melt additive containing polymer surfaces response to water or heat application and impact surface properties and composition.

Gas plasma sterilization offers a very promising alternative to conventional sterilization processes, particularly for polymer-based materials that are heat-sensitive. Plasma sterilization activity in low-pressure chambers is well known and commercial devices are available. Recent research [1-7] has successfully demonstrated the sterilization activity of atmospheric glow discharge plasma with laboratory devices.

New atmospheric plasma systems (APT) have been developed for a web treatment of textiles and non-wovens, increasing wettability, printability and adhesion properties of the surface [8]. Here we report on the possibility of destruction of microbials on exposed textile surfaces carried out utilizing these atmospheric cold plasma treatments. Preliminary investigations were performed on polypropylene [9]. A wet polypropylene nonwoven wipe was inoculated with 3. 107 colony-forming units CFU per fiber swatch of Escherichia coli (E. coli) strains. The wipe was subsequently exposed to several atmospheric plasma discharge power densities utilizing an oxygen-based plasma chemistry. The plasma species bombard the microbials to the point where experimental samples had no detectable bacteria or few colony-forming units. A second step involving a combination of E. coli strains and spores at a higher power density is under consideration to achieve a very high disinfecting effect, near sterilization, in a moving web process.

We presented several papers in improving the surface properties including the increase of wettability and sterilization by exposing the nonwoven fabrics to one atmosphere uniform glow discharge plasma (OAUGDP) using the stationary parallel plate capacitive electrodes, developed in the plasma lab at the University of Tennessee, with the application of different working gases. Recently, we constructed a continuous treating process using rotating drums with the gas feeding system. This process in contrast to the stationary plate electrodes can continuously feed the fabrics and make more uniform treatment of the nonwoven fabrics and is applicable for the industrial production. We will present the basic theory behind the generation of uniform glow discharge under one atmosphere pressure. The results of hydrophilicity, hydrophobilicity, and the ability of the nonwoven fabrics to repel the oil and the alcohol of the nonwoven fabrics will be presented. The types of the working gases, the treatment time and the duration of these properties with the shelf time will also be addressed.